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Acardiac twinning is a rare anomaly of monochorionic twin pregnancies. Acardiac fetuses lack a functional heart but are passively perfused by arterial blood from their pump co-twin causing the acardiac body to be hypoxemic. In this report, we present an acardius anceps, therapeutically laser separated from its pump twin at 16 weeks. The healthy pump twin and macerated acardiac body were born at 40 3/7 weeks. A three dimensional (3D) reconstruction was made by CT images, showing cranial bones, spinal column, pelvis and lower extremities but absent arms. A cyst in the neck of the acardiac twin was identified by postnatal sonography; this was also described in four literature cases, and was additionally observed by us in two other acardiac twins. Median cleft palate was identified by oral cavity inspection but undetectable in the reconstruction. In the literature, we found 21 other acardiac anceps twins with a cleft palate. From the two larger published series, with 12 clefts in 21 acardiac anceps twins, a cleft palate occurs in over 50% during acardiac twinning. Our first hypothesis is that acardiac fetuses develop an oral cleft palate when acardiac onset starts prior to 11 weeks, because 11 weeks includes the period of embryonic oral cavity formation, and no cleft occurs when onset starts later than 11 weeks. Our second hypothesis is that cysts and cleft palates are more common in acardiac twins than currently known, likely reflecting that acardiac bodies are hypoxemic and that hypoxia contributes to the development of both cysts and clefts., (© 2019 Wiley Periodicals, Inc.)

In this article, we provide a comprehensive overview of multiple facets in the puzzling genesis of symmetrical conjoined twins. The etiopathogenesis of conjoined twins remains matter for ongoing debate and is currently cited-in virtually every paper on conjoined twins-as partial fission or secondary fusion. Both theories could potentially be extrapolated from embryological adjustments exclusively seen in conjoined twins. Adoption of these, seemingly factual, theoretical proposals has (unconsciously) resulted in crystallized patterns of verbal and graphic representations concerning the enigmatic genesis of conjoined twins. Critical evaluation on their plausibility and solidity remains however largely absent. As it appears, both the fission and fusion theories cannot be applied to the full range of conjunction possibilities and thus remain matter for persistent inconclusiveness. We propose that initial duplication of axially located morphogenetic potent primordia could be the initiating factor in the genesis of ventrally, laterally, and caudally conjoined twins. The mutual position of two primordia results in neo-axial orientation and/or interaction aplasia. Both these embryological adjustments result in conjunction patterns that may seemingly appear as being caused by fission or fusion. However, as we will substantiate, neither fission nor fusion are the cause of most conjoined twinning types; rather what is interpreted as fission or fusion is actually the result of the twinning process itself. Furthermore, we will discuss the currently held views on the origin of conjoined twins and its commonly assumed etiological correlation with monozygotic twinning. Finally, considerations are presented which indicate that the dorsal conjunction group is etiologically and pathogenetically different from other symmetric conjoined twins. This leads us to propose that dorsally united twins could actually be caused by secondary fusion of two initially separate monozygotic twins. An additional reason for the ongoing etiopathogenetic debate on the genesis of conjoined twins is because different types of conjoined twins are classically placed in one overarching receptacle, which has hindered the quest for answers. Clin. Anat. 32:722-741, 2019. © 2019 Wiley Periodicals, Inc., (© 2019 The Authors. Clinical Anatomy published by Wiley Periodicals, Inc. on behalf of American Association of Clinical Anatomists.)

Conjoined twins represent an interesting nutritional challenge as nutrient delivery and absorption is greatly affected by anatomy and, therefore, unique to each twin pair. Nutritional support is essential to optimize growth and development in the neonatal period; however, very little data exists on the topic in this population. Conjoined twins require individualized nutritional assessment that focuses on the interaction between the metabolic rate, nutrient uptake, and nutrient delivery of each twin in the dyad. This report describes one center's experience with monitoring growth, establishing nutrient requirements, and determining substrate utilization in three sets of conjoined twins., (Copyright © 2018. Published by Elsevier Inc.)

The rarity and complexity of conjoined twins creates a challenge for prenatal planning, delivery resuscitation, and postnatal management. The modality of simulation offers a safe practice environment for a multidisciplinary group consisting of neonatal providers, nurses, respiratory therapists, and surgeons in which to identify and address clinical decision making, procedural, and behavioral plans related to routine and emergency care of these patients. Simulation-based clinical rehearsals (SbCR) provide a unique opportunity to prepare for rare, complex, and patient specific clinical procedures and scenarios. This primer serves as a revisable tool that promotes the development of proper timing, technique, and confidence to allow for an optimal setting for delivery of safe care to conjoined twins. We describe the development and implementation of a simulation approach to all stages of care from the antenatal life, NICU care, to preparation for postnatal separation of conjoined twins., (Copyright © 2018. Published by Elsevier Inc.)

Sharing of the vascular system in conjoined twins creates pharmaceutical dilemmas that require individualization of protocols. One of the major goals for the medical team is to determine how medications should be administered, dosed, and monitored in each set of conjoined twins. In order to achieve these goals, the team must determine the extent of shared circulation, volume of distribution, effectiveness of enteral absorption, renal clearance, and develop processes to ensure medication safety. In this article, we discuss unique challenges in medication practices in conjoined twins and present general principles that can be applied to determine optimal pharmaceutical strategies., (Copyright © 2018. Published by Elsevier Inc.)

The management of conjoined twins is complex and requires careful preparation. Pre-birth management includes prenatal counseling, which is important due to the overall poor prognosis. In instances of trial of life, the delivery must be tailored to address the anticipated anatomy based on prenatal imaging and anticipated physiology. A multidisciplinary team is essential to anticipate and address the ergonomic challenges and medical issues related to organ fusion, cross-circulation and associated anomalies. There are several suggested modifications to the current Neonatal Resuscitation Program algorithm including modifications to initial assessment, airway management, administration of chest compressions, obtaining emergency access, and medication dosing. Simulation is essential to address challenges, practice Neonatal Resuscitation Program modifications, delineate clear roles during delivery and practice communication. This paper offers a discussion of unique issues associated with delivery of conjoined twins and recommendations on how to approach these challenges based on our experience and available literature., (Copyright © 2018. Published by Elsevier Inc.)

Traditional nursing care strategies may require modification to meet the unique needs of conjoined twins. Here we discuss the strategies found to be useful in planning for and responding to distinctive circumstances encountered throughout hospitalization, as well as lessons learned. Areas of focus include ensuring privacy, designing adequate unit accommodations to meet space and equipment needs, staffing considerations and adaptations to typical neonatal intensive care nursing interventions. The utility of a team-based approach to interdisciplinary care coordination is also discussed. With adequate preparation and thoughtful innovation, most tertiary neonatal intensive care units can readily adapt to the unique needs of conjoined twins., (Copyright © 2018. Published by Elsevier Inc.)

Conjoined twins are a rare occurrence that offer unique challenges and circumstances to therapists. The overall goal of physical and occupational therapy treatment is to provide care that promotes developmental progression to two conjoined individuals with distinct personalities and potentially different physical and medical needs. The unique presentation of conjoined twins must be considered in determining therapeutic goals, interventions and plans of care. Providing therapeutic interventions throughout the NICU stay is a dynamic, evolving process, which challenges the therapy team to work together to find solutions. This paper aims to highlight the considerations, challenges, and strategies used to address barriers in the therapeutic care of conjoined twins., (Copyright © 2018. Published by Elsevier Inc.)

Reported here is a case of conjoined twins presented to ante-natal outpatient department of Paropakar Maternity and Women's Hospital on 21st August 2015 on a 20 year "Primigravida at 27 weeks and 6days of gestation not in labor" referred from a polyclinic following ultrasonography diagnosis for better management. After confirming the diagnosis and counseling the patients regarding mode of delivery and possible outcomes, elective caesarean section was performed and delivered male conjoined twins of Parapagusdicephalus type with poor Apgar score. No resuscitation attempted except oxygen supplementation as per wish of parents and early neonatal deaths occurred at one hour of life. Keywords: conjoined twins; monozygotic twins; siamese twins; twinning; twin pregnancy.

Conjoined twins occur in up to 1 in 50,000 live births with approximately 18% joined in a pygopagus configuration at the buttocks. Twins with this configuration display symptoms and carry surgical risks during separation related to the extent of their connection which can include anorectal, genitourinary, vertebral, and neural structures. Neurophysiologic intraoperative monitoring for these cases has been discussed in the literature with variable utility. The authors present a case of pygopagus twins with fused spinal cords and imperforate anus where the use of neurophysiologic intraoperative monitoring significantly impacted surgical decision-making in division of these critical structures.

Background: Benirschke postulated that acardiac twinning occurs when markedly unequal embryonic splitting combines with arterioarterial (AA) and venovenous placental anastomoses. We tested this hypothesis by model simulations and by comparison of outcomes with 18 "pseudo-" (twin fetus with beating heart but otherwise with clear signs of an acardiac) and 3 "normal" acardiac cases., Methods: The smaller/larger cell volume ratio at embryonic splitting becomes the smaller/larger embryonic/fetal blood volume ratio (a). From a, we derived nonpulsating blood pressures using normal values (larger twin) and normal values at an appropriate earlier gestational age (smaller twin). These unequal pressure sources were used in a linear resistance fetoplacental network to calculate umbilical venous diameter ratios. Acardiac onset occurs when the smaller twin has 50% left of its normal, singleton placenta. Comparison with clinical cases approximated a by crown-rump-length-ratio to the 3rd power. Input parameters are a and the AA-radius at 40 weeks., Results: Acardiacs can be small or large, can occur early or late, earlier at smaller a and larger AA, with larger umbilical venous diameter ratios at smaller a and smaller AA. Comparison with the 21 clinical cases was good, except for 2., Conclusion: Our analysis supports Benirschke's hypothesis. The smaller twin has to share its placental perfusion with the larger twin, which is a novel finding. The AA size is essential for the future of both fetuses but complicates easy understanding of (pseudo-)acardiac clinical presentations. Late acardiac onset occurs infrequently. Using nonpulsating circulations may have caused our extensive predictions of late onset. An improved model requires including hypoxemia in the smaller twin from chronic placental hypoperfusion. Birth Defects Research 109:211-223, 2017. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Background: Diprosopus is a subtype of symmetric conjoined twins with one head, facial duplication and a single trunk. Diprosopus is a very rare congenital anomaly., Methods: This is a systematic review of published cases and the presentation of two new cases born in Argentina. We estimated the prevalence of conjoined twins and diprosopus using data from the National Network of Congenital Anomalies of Argentina (RENAC)., Results: The prevalence of conjoined twins in RENAC was 19 per 1,000,000 births (95% confidence interval, 12-29). Diprosopus prevalence was 2 per 1,000,000 births (95% confidence interval, 0.2-6.8). In the systematic review, we identified 31 diprosopus cases. The facial structures more frequently duplicated were nose and eyes. Most frequent associated anomalies were: anencephaly, duplication of cerebral hemispheres, craniorachischisis, oral clefts, spinal abnormalities, congenital heart defects, diaphragmatic hernia, thoracic and/or abdominal visceral laterality anomalies. One of the RENAC cases and three cases from the literature had another discordant nonmalformed twin., Conclusion: The conjoined twins prevalence was similar to other studies. The prevalence of diprosopus was higher. The etiology is still unknown. The presence of visceral laterality anomalies may indicate the link between diprosopus and the alteration or duplication of the primitive node in the perigastrulation period (12-15 days postfertilization). Pregnancies of more than two embryos may be a risk factor for diprosopus. Given the low prevalence of this defect, it would be useful to perform studies involving several surveillance systems and international consortiums. Birth Defects Research (Part A), 2016. © 2016 Wiley Periodicals, Inc. Birth Defects Research (Part A) 106:993-1007, 2016. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Given the uniqueness of the Hungarian conjoined twin sisters Helen and Judith (1701–1723) and their lasting influence as an anatomical showcase if not model for mental or social deviant states, we present here a closer scrutiny of their introduction into the scientific literature of the later 18th century by analyzing depictions of the twins from 1707 onwards.

This paper presents a history of the treatment of conjoined twins. The first mention of this malformation comes from the Neolithic period. Conjoined twins were depicted in mythologies of ancient peoples. The present paper focuses on the theories of formation of Siamese twins and attempts at their separation. Moreover, the history of treatment of conjoined twins in Poland is described.

Conjoined twinning is one of the most uncommon congenital anomalies. Maintenance in an intensive care setting during this time allows for close monitoring, stabilisation, and nutritional supplementation of the infants as necessary to optimise preoperative growth and development. The birth of conjoined twins is a very difficult and dramatic moment for parents. It is also a very difficult situation for the team of physicians, nurses and other required hospital staff to carry out treatment and care of these specific developmental anomalies. The diagnostics and treatment in this extraordinary situation requires close cooperation of the multidisciplinary medical team, which includes their personal experience and medical knowledge, with a team of intensive care unit nurses. This report presents the rules in cease of conjoined twins during their intensive care unit stay with special reference to the proceedings before and after complete separation.

Congenital duplication anomalies occasionally occur in both humans and animals. Although various forms of classification of these conjoined twins exist, each case should be considered as an individual. In the case study presented a Holstein Frisian calf, born alive after 281 days of normal gravidity was investigated by computed tomography (CT) and subsequent dissection. The calf could be classified as a parapagus dicephalus tetrabrachius. It exhibited two heads each of them with a complete cervical spine leading to a complete thoracic and lumbar spine and separate tails. Looking at the point of fusion, the twin was conjoined in the ventrolateral thoracic part of the body. The calf had two thoraces with four forelimbs and two pelvic limbs on a single pelvis. As two heads and thoraces were present, beginning at the oral cavity, two intestinal systems were observable leading to a fusion point at the ascending part of the duodenum been continued caudally as a single system. Within each thorax, two lungs and a heart were present. However, only the heart in the left thorax was normal shape, exhibiting a strong myocardium and increased size. In contrast, the heart within the right thorax was considerably smaller, round shaped, and it appeared to be spongy and not fully developed during the foetal period. Commonly, classification of conjoined twins is only based on the appearance of the skeletal system. However, in the case presented, the point of fusion of the skeletal system did not allow conclusions regarding the intestinal or cardiovascular system., (© 2013 Blackwell Verlag GmbH.)

The purpose of this case report was to describe oral findings and outline challenges and considerations for general anesthetic (GA) and dental management of 4-year-old female craniopagus (cranially conjoined) twins, at high risk for medical comorbidity, who presented for treatment of severe early childhood caries. This hospital-based procedure required good interdisciplinary communication, cooperation, and presurgical planning to address unique challenges and ensure positive postoperative outcomes. Two separate anesthesia teams delivered GA simultaneously to each twin. To minimize anesthetic exposure, two pediatric dental teams completed dental care concurrently. Extensive plaque accumulation and unusual "mirror-image" caries distribution were attributed to frequency and postural pooling during feeding. The rehabilitation objective was to provide definitive dental management, minimizing future need for dental retreatment under GA. Two-month follow-up revealed intact dental restorations, good oral hygiene, and weight gain. For these unique twins however, the challenge of long-term oral health maintenance remains.

A case of female parapagus conjoined twins living as unseparated is presented in this report. The twins had two heads, four arms and two legs. As a result of their fusion, operative care had been considered to be unacceptable, and the family had refused to take care of them. At three years of age, they were referred to the Rehabilitation Department with the complaint of inability to walk. While designing the rehabilitation program, somatosensory evoked potential evaluation was performed and showed that twin 1 controlled the right leg and twin 2 controlled the left. The program consisted of coordinated pacing training by verbal commands, upper and lower extremity reeducation, and balance and coordination exercises. After two months of inpatient rehabilitation, they were able to walk independently with a specially designed walker. Currently, the twins are 11 years old with normal academic achievement, and they are able to walk, run and climb the stairs independently.

This study aimed to identify the anatomic and pathologic structural cardiac abnormalities in conjoined twins and to focus on those that have prevented the successful separation of conjoined hearts. A retrospective review was undertaken to examine consecutive cases of thoracopagus conjoined twins with conjoined hearts evaluated at The Children's Hospital of Philadelphia from 1 January 1980 through 6 October 2008. The records included autopsy and surgical findings as well as clinical reports. The study group included nine sets of conjoined twins with a mean gestational age at birth of 33.8 ± 5.5 weeks. Three twin pairs were stillborn. Five twin pairs died afterward. One pair died of cardiopulmonary failure. The median age at death was 22 days (range, 0-345 days). Major congenital heart disease was present in 94.4% (17/18) of the hearts, and 72.2% (13/18) of the hearts had single-ventricle physiology. Total anomalous pulmonary venous return occurred in 39% (7/18) of the cases. The clinical outcome for thoracopagus twins with conjoined hearts remains poor because of inability to separate conjoined and single ventricles. Surgical nonintervention and palliative care should be strongly considered for these patients.

Introduction: Conjoined twinning is an extremely rare anomaly. Very few diagrammatic descriptions are provided for the various hepatobiliary anomalies seen in these twins. We aimed to review our experience with the various subtypes of hepatobiliary anomalies and their association with the inability to separate as well as provide diagrammatic descriptions of these anomalies., Methods: We retrospectively reviewed our experiences within separating twins. We reviewed patterns of hepatobiliary anomalies and the required investigations and intraoperative workups., Results: Of the 60 cases we evaluated, 28 were successfully separated. The reasons for nonseparation were possession of: a single heart, major communicating hearts, or major chromosomal anomalies. The liver was involved in 17 cases (60.7%) in the operative group and 23 cases (71.8%) in the nonoperative group. All cases had a computed tomographic scan and ultrasound as preoperative workup. Only 2 cases required a magnetic resonance cholangiopancreatography for preoperative evaluation. Intraoperative ultrasound was not used, and only 3 cases required an intraoperative cholangiogram. Diagrammatic depictions of the various categories of anomalies are presented., Conclusion: In our experience, we did not find hepatobiliary anomalies to be the sole reason for inseparability in any of the conjoined sets. Hepatobiliary anomalies seem to be more frequent in the nonseparable group., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Twin pregnancy is associated with a high risk of congenital malformations. This review covers the risk of such anomalies in both dizygotic and monozygotic twin pregnancies, and discusses current insights into the associations relating to zygosity, chorionicity and genetic factors. The pathological basis of specific malformations unique to the monochorionic twinning process, including conjoined twinning and twin reversed arterial perfusion (TRAP) sequence, is discussed in more detail, and factors contributing to the higher perinatal mortality rate in multiple pregnancies are addressed., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Heteropagus, or "parasitic," twins are asymmetric conjoined twins in which the tissues of a severely defective twin (parasite) are dependent on the cardiovascular system of the other, largely intact twin (autosite) for survival. The estimated incidence of heteropagus twins is approximately 1 per 1 million live births. Isolated case reports comprise most of published work on this rare congenital anomaly. In the past, review articles have focused narrowly on one particular anatomical subtype of parasitic twin and/or on the anatomicopathology observed. Here, we present the epidemiology, proposed pathoembryogenic origins, anatomical abnormalities, management, and outcomes of the wide array of heteropagus twins described in the English language literature., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Background: Conjoined twins represent a rare case of embryonic failure. Siamese twins' final outcome is usually associated with poor prognosis due to complications, among which the inflammatory and septic disturbances are often present., Case Report: The article describes Siamese twins of craniopagus type. One of the twins died of heart and aortic failure after 48 hours of life. The decision regarding surgical separation then became an emergency. At the same time laboratory results for the surviving twin I indicated steadily worsening coagulation functions and processes, which we believed were caused by the death of twin II, as well as by systemic inflammatory response syndrome (SIRS)., Conclusions: Due to vascular conjunction between the twins' brains' circulatory systems the sequenced progress of coagulopathy was noticed in the surviving twin.

Purpose: The aim of the study was to analyze the frequency and certain epidemiological characteristics of a consecutive series of conjoined twins born in Spain., Material and Methods: We used data from the Spanish Collaborative Study of Congenital Malformations for the period April 1976 to 2006. Because the Spanish law permitting voluntary termination of pregnancies (TOP) when the fetus presented malformations was effective by the end of 1985, we analyzed the data in 4 periods, 2 before 1986 and 2 after. During the first period (1976-1979) only live births were recorded, whereas both still and live births were included in the other three (1980-1985, 1986-1995, and 1996-2006). In the present study, the cases were classified as symmetrical (16 pairs) and asymmetrical (1 pair) conjoined twins. Each pair of conjoined twins was considered as only one case for calculations, regardless of the type of union., Results: Among a total of 2,281,604 consecutive births between 1980 and 2006, there were a total of 15 cases of symmetrical conjoined twins giving a frequency of 0.70 per 100,000 (1/152,107), whereas there was only 1 stillborn asymmetrical conjoined twin pair (0.04/100,000). Among the 13,418 consecutive stillborns surveyed, 6 cases of conjoined twins were identified (either symmetrical or asymmetrical) giving a frequency of 44.72 per 100,000, and 11 pairs were identified among the 2,425,583 total live births surveyed during the first period 1976 to 1979, a frequency of 0.45 per 100,000. Thus, the frequency among stillborn infants is 99.34 times higher than that observed among live births. However, the frequency for the total births (3 last periods) showed a decreasing trend from 1.47 per 100,000 birth in the first period (1980-1985) when TOP was illegal, to a value of 0.09 per 100,000 in the last period, more than 16-fold lower, probably because of the TOP of affected fetuses. Therefore, we consider that the frequencies observed in the period 1980 to 1985 are the basal values in our population. The most frequent type observed was thoracopagus, with an overall prevalence at birth of 0.44 per 100,000 (1/228,160) from 1980 to 2006, representing 58.82% of the total population of symmetric conjoined twin pairs. Diprosopus pairs were the next most common group (11.76%). Most of the cases were females (4 males/11 females), and although this appeared to be mainly because of the thoracopagus pairs (males-females, 2:8), in such a small number of cases, it is not possible to determine the ratios for the other groups. Gestational age was significantly shorter than in control twins for each type studied., Conclusions: We conclude that it is incorrect to consider that all types of conjoined twins have the same epidemiological characteristics, such as the frequency at birth. The differences observed may be related with the distinct embryo-fetal mortality of each type of conjoined twins in different populations, and the sex ratio, among others.

Heteropagus twin refers to a type of conjoined twin in which an incomplete smaller (parasitic) twin is attached to and dependent upon an otherwise normal host twin. The majority of cases have complete or partial duplication of the pelvis and/or lower extremities. The case depicted herein is unusual in that only isolated case reports have described an attached amorphous mass without identifiable limbs.

Conjoined twins represent a rare form of incomplete embryonic separation. They are classified into eight different subtypes, with 18% representing pyopagus conjoints. History is scattered with accounts of the various types of conjoints and it is only recently that strategies have been devised to enable surgical separation of such twins. It is estimated that approximately 20 cases of separation of pyopagus twins have been performed. We provide a historical look at pyopagus conjoint twins and report our neurosurgical experience of Australasia's first separation of pyopagus twin girls.

We describe the anaesthetic management of a pair of thoracopagus twins of 14 months of age undergoing complex cardiac evaluation. Synchronous ventilation of the twins, needed for the ECG-gated magnetic resonance imaging-angiography, was achieved through a Carlens (Y) adaptor during procedures and transport. The complex logistical implications are obvious. We also describe the first use of bispectral index monitor for detection of cross-circulation in conjoint twins.

We report a case of thoracopagus twins undergoing magnetic resonance imaging (MRI) studies under general anesthesia. The twins had a complex shared cardiac anatomy that posed additional challenges to an already-difficult anesthesia care area. This report emphasizes the approach to anesthetic management of conjoined twins in the MRI environment.

Thoraco-omphalopagus conjoined twins born to a 25-year-old para one Ethiopian lady are presented. Prenatal diagnosis was not made until elective cesarean section delivery was done for severe preeclampsia and twin pregnancy with breech presentation. Detailed autopsy results and relevant literature reviews are described. To the best of our knowledge, these are the second-documented cases of conjoined twins in this country.

A thirty-eight year old, gravida seven, para six mother presented to the outpatient department of Saint Paul's General Specialized hospital on September 11, 2003 after attempted delivery of the shoulder failed at Meta Robi health center. Referral note indicated that she presented at the health center in the second stage of labor, which was delayed for more than two hours. Ventouse delivery was effected at the health center following which the shoulder could not be delivered and mother was referred to Addis for further management of the shoulder dystocia. Upon presentation to the hospital further delivery of the fetus was difficult and an ultrasound exam showed a twin pregnancy. A caesarean delivery was effected with the possibility of conjoined twinning. Stillborn 5100 grams thoracopagus twins were delivered with intraoperative decapitation of the head of the vaginally delivered twin. Mother was discharged after seven days in good condition. Literature on the diagnosis and management of conjoint twinning is reviewed and the rare situation in which a conjoined twin might be a differential diagnosis of shoulder dystocia is noted.

Introduction: Attention is drawn to the spontaneous incidence of twinning, both dizygotic and monozygotic in different mammalian species. Conjoined twinning, however, only arises when the twinning event occurs at about the primitive streak stage of development, at about 13-14 days after fertilisation in the human, and is exclusively associated with the monoamniotic monochorionic type of placentation. It is believed that the highest incidence of conjoined twinning is encountered in the human. While monozygotic twinning may be induced experimentally following exposure to a variety of agents, the mechanism of induction of spontaneous twinning in the human remains unknown. All agents that are capable of acting as a twinning stimulus are teratogenic, and probably act by interfering with the spindle apparatus., Discussion: The incidence of the various types of conjoined twinning is discussed. Information from the largest study to date indicates that the spontaneous incidence is about 10.25 per million births. The most common varieties encountered were thoraco-omphalopagus (28%), thoracopagus (18.5%), omphalopagus (10%), parasitic twins (10%) and craniopagus (6%). Of these, about 40% were stillborn, and 60% liveborn, although only about 25% of those that survived to birth lived long enough to be candidates for surgery. Conjoined twinning occurs by the incomplete splitting of the embryonic axis and, with the exception of parasitic conjoined twins, all are symmetrical and "the same parts are always united to the same parts". Fusion of monozygotic twins is no longer believed to be the basis of conjoined twinning. Accounts are provided of the anatomical features of each of the commonly encountered varieties.

The Red Cross War Memorial Children's Hospital, Cape Town, South Africa is the only dedicated children's hospital in sub-Saharan Africa and, as such, is the referral hospital for complex procedures from this region. Fifteen sets of conjoined twins have presented for separation from 1991 to 2002, and a total of 34 sets since 1964. Anaesthesia for procedures on conjoined twins is a demanding, exacting and meticulous exercise, whether prior to or during separation. Anaesthesia forms part of the multidisciplinary management of the babies. Emphasis is laid on preoperative assessment, goal-directed planning of theatre and the staff involved in the surgery, duplication of all equipment necessary for anaesthetizing and monitoring two infants in one operating room, and having plans in place to avoid overcrowding. Challenges encountered in anaesthesia for these twins include identifying anatomical conjunctions, airway management, acquiring vascular access, the potential for enormous blood loss, and maintaining normothermia. Planning for the postseparation period and the reconstruction and rehabilitation of the babies is essential from the time of their initial admission. Meticulous attention to detail, monitoring and vigilance are mandatory. Successful management of conjoined twins relies on close communication and cooperation of all members of the multidisciplinary team.

Objective: To examine the possible role of calcium in conjoined twinning., Study Design: Conjoined (CJ) twins are an extreme example of monozygotic (MZ) twinning. Data were collected from various sources on factors to which gravidas who deliver CJ twins were exposed around the time of conception., Results: A significant number of such women were subjected to environmental triggers. Of particular interest is increased CJ twinning following use of oral contraceptives. It is hypothesized that this resulted from prolonged ovulatory dysfunction in lightweight women. The incidence of uniovular twinning is inversely related to women's prepregnancy weights., Conclusion: These observations are consistent with the proposed general model of MZ twinning. Factors that induce calcium depression and delayed implantation encourage uniovular duplication in general and CJ twinning in particular.

Conjoined twins represent the most uncommon twinning mechanism in humans, with an incidence approaching 1:100,000 deliveries. Although several conjoined male twins have occasionally been reported, for unexplained reasons most cases of conjoined twins are female. Of all the female conjoined twin sets either documented by medical authorities or referenced in ancient literary sources, in only one case were pregnancy and delivery successfully achieved by the conjoined twins themselves. We describe the highly unusual circumstance of the Blazek sisters, an extreme developmental example of the terminal monogenital pygopagus type of conjoined twins in which one of the joined sisters conceived and underwent labor and childbirth. Although little information is known about their own birth, these conjoined twins paradoxically hold a unique place in the history of obstetrics. Information from formal anatomic examinations of the sisters and their exploitative circus exhibitions is outlined with a view to explain relevant reproductive events. We present the sensational conception, pregnancy course, and subsequent vaginal delivery of a healthy male infant as summarized from contemporary sources. Additionally, the significance of pygopagus twins is discussed with regard to other types of monozygous twinning. Although modern operative techniques have been a welcome advance in the science of conjoined twin separation, the Blazek case is another reminder that, even in the era before complex surgery, conjoined twins were not necessarily consigned to an incomplete reproductive career.

During the course of researching the embryologic etiology of conjoined twins, more than 1260 individual cases were collected from the literature and the reported abnormal anatomy tabulated and evaluated in the light of known embryology. It soon became apparent that the association of conjoined twins and their parasites with fetuses in fetu, acardiacs, and teratomas was more frequent than could be attributed to chance. These anomalous fetuses form a continuum, strongly suggesting that they are all variations of abnormal conjoined twinning, with the site of union and the extent of damage (or defect) of one embryo resulting in (1) an externally attached parasitic twin, (2) an enclosed fetus in fetu, (3) an internal teratoma, or (4) an acardiac connected via the placenta. Common patterns among them are a family history of twinning, the predominance of females, and the frequent presence of a twin or triplet accompanying the malformation. The several reports of chromosomal abnormality suggest that perhaps, at least on occasion, it is a genetically imperfect embryo that develops into a defective fetus. Of singular importance is the fact that rarely, if ever, is either a functional heart or a competent brain found in any of these abnormal fetuses, suggesting that the etiology of all of them is a primary cardiac malformation with secondary disruption in the development of the brain., (Copyright 2001 Wiley-Liss, Inc.)

Purpose: To describe the anesthetic management of newborn omphalopagus conjoined twins undergoing a series of diagnostic and surgical procedures which culminated in successful separation at one month of age., Clinical Features: Evaluations of the extent of shared organ systems were carried out without the need for anesthesia. The twins were anesthetized twice, once for insertion of skin expanders, and later for surgical separation. Various airway management techniques were utilized. To facilitate surgical separation, caudal epidural catheters were inserted in an effort to provide both operative and post-operative analgesia. In addition, prior to the induction of anesthesia, the extent of cross-circulation between twins was assessed., Conclusion: Caudal epidural catheters can be used to provide both operative and post-operative analgesia. Early extubation, another benefit of regional analgesia, was not achieved because both twins developed respiratory failure in the immediate postoperative period. Testing for the extent of cross-circulation between twins proved valuable, allowing for detailed scripting of the complex induction sequence and airway management.